Cation-pi cyclizations initiated by the disrotatory electrocyclic opening of cyclopropanes are being studied as a general method for the synthesis of alicyclic and heterocyclic compounds. The utility of this new synthetic strategy is being demonstrated in versatile total syntheses of antimicrobial. antitumor sesquiterpene lactones. The application of this approach to the synthesis of nitrogen heterocycles is being illustrated in short total syntheses of perhydrohistrionicotoxin and anatoxin a.